Electrolytic acidic solution for cadmiating of various parts

ABSTRACT

ELECTROLYTIC ACIDIC SOLUTION FOR CADMINATING OF VARIOUS PARTS CONTAINING, IN AN AQUEOUS DEMINERALISED CARRIER, A CADMIUM SALT, A FREE ACID, A BRIGHTENING AGENT SELECTED FROM THE CLASS CONSISTING OF A SEMITHIOCARBOZONE COMPOUND ATTACHED TO A THIOUREA GROUP AND A DITHIOCARBAMIC ACID CONDENSED WITH ALDEHYDE PHENOL, AND A WETTING AGENT INDIIFFERENTLY SELECTED AMOUNG NONIONIC, CATIONIC OR ANIONIC WETTING AGENTS.

United States Patent M U.S. Cl. 204-50 R 6 Claims ABSTRACT OF THE DISCLOSURE ,Electrolytic acidic solution for cadmiating of various parts containing, in. an aqueous demineralised carrier, a cadmium salt, a free acid, a brightening agent selected from the class consisting of a semithiocarbazone compound attached to a thiourea group and a dithiocarbamic acid condensed with aldehyde phenol, and a wetting agent inditferently selected among nonionic, cationic or anionic wetting agents.

This is a continuation of application Ser. No. 102,555 filed Dec. 29, 1970, now abandoned.

It is known that in many industries, for instance, in screw-cutting, smaller machinery, electronics, aeronautics, etc., it is known that we generally use cyanide-electrolyte for obtention of cadmium coating because acidic electrolytes have not yet madeit possible to achieve any penetrating and bright platings. It is also known that the utilization of such baths based on cadmium cyanide gives rise to difficulties with respect to waste water processing. Moreover, cyanide-containing baths embrittle high yield strength steels, and as a result thereof, processed parts made of such type of steel have to undergo a degasing treatment which is often difiicult to carry out or even ineifective.

It is a purpose of this invention to overcome largely with these difficulties.

According to this invention, aqueous acidic electrolytes containing cadmium salts are added with organic additives which permit to obtain bright and penetrating cadmium coatings. Use of such acidic baths eliminates the necessity of especially treating waste water and makes high yield strength materials less brittle. Another object of this invention is to introduce in connection with the brightening agent other elements which increase the penetrating power of baths.

The acidic electrolyte according to this invention is characterized in that it principally contains:

a cadmium salt such as cadmium sulphate;

a free acid such as sulphuric acid; and

a thiosemicarbazone compound representing the brightening agent of the general formula \NH-N=CHR prepared for instance by the action of phenol aldehyde on a thiosemicarbazide derivative, more particularly of piperonal on thiosemicarbazide, to which compound a thiourea group NH CS-NH is attached, R preferably being the carbon-chain of a phenol aldehyde or heteroxid derivatives thereof.

The attachment of thiourea group can be effected as well on the phenol aldehyde before conversion into thiosemicarbazone as on the thiosemicarbazone compounds as defined thereabove. The utilization of thiosemicarbazone, however, is not given as a limitation, and a dithiocarbamic acid-phenol aldehyde condensate could also be used with- 3,826,722 Patented July 30, 1974 out departing from the scope of the invention. By way of example, phenol aldehyde in aqueous-alcoholic medium in the ratio of 1:1 is reacted with thiourea in the molar ratio of 1:1 during about 4 hours, the thiosemicarbazide is prepared also as a solution in an aqueous-alcoholic medium in the ratio of 1:1 and this solution is added to that product which has been obtained in the first reaction, these operations being carried out at a temperature of about 30 C. during about 2 hours.

The brightening agent thus obtained can either be used directly or after a purification. In the second case, the final condensation product dissolved in aqueous alcoholic medium is precipitated by addition of a volume of water which amounts to 5 to 6 times the initial volume. After filtering and washing on the filter with a little alcohol amount the precipitate is dissolved again into a solvent which may be a mixture of alcohol and acetone.

The electrolyte also contains added substances which make it possible to extend the brightness range, i.e. the ability to use current densities within a relatively large range, for instance between about 0.1 and 5 A./dm. Said added substances can be used in conjunction with the thiosemicarbazone compound mentioned above. Among these products, it is possible to use alone or an association non-ionic wetting agents such as derivatives of fatty alcohols and of ethylene oxide or of fatty acids and ethylene oxide or of alkylphenols and ethylene oxide more particularly the nonylphenol on which there are condensed from 10 to 13 ethylene oxide moles. Moreover formalin, glyoxal, benzenesulphonic acids, toluenesulphonic acids or naphthalene-sulphonic acids or the salts thereof, sulphonic acids or their benzene, naphthalene or anthracene derivatives salts such as naphthols or anthraquinones, may also be used.

More particularly, addition of sodium 2-naphthalenesulphonate conjointly with the reaction product of glyoxal with an amine gives particularly good results.

It was noted that the addition to the bath of a dior polybasic cationic surfactant obtained through condensation of a fatty acid with a polyamine, being either a dior a triamine, would also increase the brightening range.

Anionic surfactants as for instance sulphated alcohols or salts thereof can also be used in. the electrolyte composition instead of or in association with non-ionic surfactants described above.

In order to indicate still more fully the nature and utility of the invention the following examples of preferred electrolyte compositions containing the components according to the invention are set forth, it being understood that these examples are presented as illustrative only and that they are not intended to limit the scope of this invention.

The following examples of electrolyte compositions are as well adapted to the electroplating of parts charged in bulk in a rotating drum as to that of parts fixedly held in a bath. 7

. Example I In order to brighten screws contained in bulk in a drum having a rotation speed of substantially 10 rpm. and a capacity of 50 kg. for treated parts, 1000 l. of an aqueous electrolyte containing G./l. Cadmium sulphate 40 Sulphuric acid 60 3 are used under following conditions:

Bath temperature 25 C. Current density 2A./dm. Anodic/cathodic surface ratio 1/2 Time of treatment 15 min. Soluble anodes cadmium.

The parts obtained according to this treatment exhibited a perfect brightness throughout their surface and were likely to get a passivity in sulphuric chrome-plating solutions.

Example II The same process as in example I was followed at the difference that 1 g./l. of octyl alcohol sulphate was substituted for the non-ionic surfactant. The results of this treatment were similar to these of said Example I.

Example III For the brightening of a television receiver frame, said frame was fixed in a bath similar to that of example I, but the cadmium sulphate content was adjusted to 60 g./l. and the current density was at 4 A./dm. for an anodic/ cathodic surface ratio of 1: 1. The time of treatment adapted to obtain a brightening grade comparable with that of example I was 8 min.

Example IV This experiment was carried out as described in example III, but 30 g./l. of cadmium metal as fluoroborate was substituted for cadmium sulphate. The results thus obtained were entirely comparable with these according to example III.

Example V This experiment was carried out as described in example I, but the wetting agent used in this case was an amount of 2 g./l. of a non-ionic surfactant of a type obtained by condensing ethylene oxide with an alkylphenol (condensation of 12 ethylene oxide moles with nonyl-phenol as reacting product).

Example VI For the brightening of a television receiver frame, said frame was fixed in an aqueous electrolyte bath contain- G./l. Cadmium sulphate 80 Sulphuric acid 80 under following reaction conditions:

Anodic/cathodic surface ratio 1 Bath temperature 20 C. Current density 3 A./dm.

Time of treatment min.

Diethylene diamine is another name for piperazine 4H10 2- i It Was noted that in carrying out the methods of preceding examples, the best results were obtained with baths, the temperature of which ranged between 18 and 25 C., with the use of demineralised water. The aqueous carrier contains the cadmium salt in a proportion from 30 to 80 g./l., the freeacid in a proportion'of from 30 to 100 g./l., the brightening agent in a proportion from 0.1 to 1 g./l. and the wetting agent in a proportion from 0.5 to 10 g./l., an electric current at a current density from 0.1 to 5 A./dm. being caused to pass through the electrolyte.

We claim: 1. An electrocadmiating acid mixture comprising an aqueous solution of an inorganic salt of cadmium in a concentration of 40 to 80 grams per liter, a free acid in a concentration of to grams per liter, and an effective amount of a thiosemicarbazone brightening agent, said brightening agent prepared byreacting piperonal in an aqueous-alcohol medium with thiourea in a 1:1 molar ratio, and reacting the product of said reaction with an aqueous-alcoholic solution of thiosemicarbazide at a temperature of about 30 C. for about 2 hours.

2. The mixture of claim 1 wherein said inorganic salt is cadmium sulfate and said free acid is sulfuric acid. 9 3. The mixture of claim 2 wherein said mixture is additionally provided with 5 grams per liter of sodium-2- naphthalene-sulfonate and 1 gram per liter of octyl alcohol sulfate.

4. A method of electrocadmiating a metal part from a bath which comprises preparing an aqueous electrolyte comprising an inorganic salt of cadmium in a concentration of 40 to 80 grams per liter, a free acid in a concentration of 60 to 80 grams per liter, and an effective amount of a thiosemicarbazone brightening agent, said brightening agent prepared by reacting piperonal in an aqueous-alcohol medium with thiourea in a 1:1 molar ratio, and reacting the product of said reaction with an aqueous-alcoholic solution of thiosemicarbazide at a temperature of about 30 C. for about 2 hours, immersing the metal part in the resulting electrolyte, and passing electric current at a current density of .1-5 A./dm.

through said electrolyte from a soluble cadmium anode to a solid cathode which is the metal part to be cadmiated.

5. The method of claim 4 wherein said inorganic salt is cadmium sulfate and said free acid is sulfuric acid.

6. The method of claim 4 wherein said electrolyte is additionally provided with 5 grams per liter of sodium-2 naphthalene-sulfonate and 1 gram per liter of octyl alcohol sulfate.

References Cited UNITED STATES PATENTS GERALD L. KAPLAN, Primary Examiner 

